This invention relates to process and apparatus for treating a harmful substance, in particular, to process and apparatus for treating dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxins.
Dioxins are referred to, for example, the following literature.
Reference 1: xe2x80x9cAn introduction to dioxinsxe2x80x9d translated by Ryota Fujiwara and Higashi Kido, edited by Masatoshi Morita, and published by JESC (Japan Environmental Sanitation Center) on June 1991 (Original document: U.S. EPA Research Reporting Series, xe2x80x9cDioxinsxe2x80x9d).
1.  less than Structure and Production Cause of Dioxins greater than 
Dioxins were synthesized at first in Germany in the mid-19th century, but their strong toxicity wasn""t known until 1950s. Ever since, the toxicity of dioxins has been widely known through the news of frequently broken out occupational diseases and environmental pollution, Vietnam War and etc. in connection with dioxins, and studied widely. In 1990s, it has been known that dioxins spread out widely around their surroundings through the incineration of refuse/waste and other processes. Consequently, studies on the influence, measurement and removal method of dioxins have been suddenly required. To attain this end, these studies have become active, and the number of papers concerning dioxins is rapidly increased now.
At first, an outline of dioxins is given below. General chemical structure of dioxins may be represented as follows. 
To the substitution sites of the numbers 1 to 4 and 6 to 9, chlorine and other halogen atoms, organic radical and hydrogen atom may be bonded. These kinds of compounds are usually called as xe2x80x9cdioxins homologuesxe2x80x9d, and 77 or more kind of isomers belonging thereto are known.
Among these dioxins homologues, the most remarkable compound in the field of environmental science and others is 2,3,7,8-tetrachlorodibenzo-p-dioxins (C12H4Cl4O2; which is abbreviated as xe2x80x9cTCDDxe2x80x9d to the 2-, 3-, 7- and 8-positions of which chlorine atoms are bonded.
TCDD has no functional group of high reactivity, thereby showing extremely high chemical stability, belongs to molecules soluble in high molecular weight paraffin, dissolves very little in water and most of organic solvents, and exhibits a colorless crystalline solid at room temperatures.
For synthesizing dioxins, various processes are known. Their reaction temperatures range from 180 to 400xc2x0 C., and the reaction products are stable up to 700xc2x0 C. Accordingly, it is necessary to apply heat up to temperatures of not less than 800xc2x0 C., or of not less than 1150xc2x0 C. under certain conditions to decompose dioxins.
Typical organic compounds potentially by-producing dioxins include chlorophenols and their derivatives; and hexachlorobenzene. These compounds are classified into the following 3 large groups.
The first: polyhalogenated phenols (1st group).
The second: o-halophenols, and halogen- and other-substituted phenols (2nd group).
The third: substances not classified into 1st and 2nd groups but possibly producing dioxins (3rd group). However, the possibility is low that the substances of the 3rd group produce dioxins.
As a material belonging to the above groups and commercially produced not less than 1,000 pounds in a year in U.S., there are known 12 kinds of chemical substances belonging to the 1st group, 16 kinds of chemical substances belonging to the 2nd group, and chemical substances of 50 kinds or so belonging to the 3rd group.
By the process for preparing pesticides such as insecticide and herbicide, dioxins are potentially by-produced. A large number of agricultural chemicals are known that contain dioxins at high concentration.
Recently, the precision of measuring dioxins has been improved to enable measuring a very small amount of dioxins. Consequently, the discovery has been made that dioxins are contained in agricultural chemicals and also in a basic chemical material of chlorophenols although the content contained in the latter material is very little. Moreover, it is known that not only these substances but also industrial wastes generated in the course of producing the same contain dioxins at high concentration. The aforementioned chemical material is used as a preservative of foods, crude rubber, leather or the like, or, otherwise as a raw material for preparing insecticides.
In addition to the above, these are applied directly to the human body in disinfecting swimming pool, home, hospital, bathroom and etc. All of these compounds are registered as an insecticide in EPA (Environmental Protection Agency) in U.S.
The fact that dioxins are produced according to the above process has been hitherto known. Recently, owing to the press and other media, attention has been paid to production and diffusion of dioxins originated from xe2x80x9ccombustion sourcexe2x80x9d, that is, waste/refuse incineration or other incinerating facilities. This finding is much owing to the improvement in the precision of measuring dioxins in Japan. However, before this time, 17 kinds of dioxins were detected by the analysis of floating particulate matter collected out of 3 municipal refuse-incinerating facilities in the Netherlands in 1977. Diffused dioxins are contained in combustion gas and fly ashes.
On the synthesis of dioxins through the step of burning, chemists of the Dow Chemical Company considered that many precursors of dioxins are produced through a complicated process such as burning, and suggested in 1978 that dioxins are synthesized naturally through the combustion of natural materials. Then, many chemical substances of the precursors have been studied until today.
It is necessary in decomposing dioxins by combustion at least to apply heat up to temperatures of not less than 800xc2x0 C. and watch whether dioxins are regenerated or not at temperatures ranging from 180 to 400xc2x0 C. when the temperature of the resultant decomposition product becomes lowered. It is also known that dioxins contained in fly ashes never decompose without heating up to around 1200xc2x0 C.
2.  less than Dioxins Analyzing Method greater than 
Because dioxins have very strong toxicity, microanalysis is required. General analyzing methods of dioxins include gas chromatography, mass spectrometry, UV spectrophotometry, ESR (electron spin resonance) spectroscopy, low temperature phosphorimetry and etc. There is no analyzing method now that can provide both high sensitivity and selectivity at the same time applicable to substantially all the samples and surroundings.
It is said that the detection limit of dioxins is about 0.001 ppb (ppb: parts per one billion) at the present time. However, fluctuations in the measured value, which are large especially at low concentration, arise depending on measuring system, person and etc. On account of this, it is important to standardize the measurement, and for attaining this purpose, a joint study is started now by plural organizations such as research institutions and universities in Japan. Through the above activities, the measurement in and of itself is accepted as one of important research and development themes.
3.  less than Dioxins Exposure Accident to the Human Body greater than 
Up to this time, there have been reported a lot of accidents caused by dioxins. Among them, an accident that happened in Meda, Italy on Jul. 10, 1976 is very terrible. In this accident, 300 g to 130 kg of dioxins were scattered around to pollute their surroundings and to cause 134 cases of children suffering from acute toxicity of chloracne. Further, 170 labors were directly polluted, and hundreds of animals were taken ill and killed in the worst case.
It is said that the largest-scale pollution which has ever happened in the world until now is the pollution caused by the United States Air Force burning 10,400 tons of a defoliant containing dioxins on the Pacific Ocean in 1977, and that this fixed the dioxins"" background of the world.
Further, it is said that the birth of many malformations found in Vietnam is due to pollution caused by spraying the defoliant. However, some U.S. report told that there is no correlation between the sprayed defoliant and the birth abnormality. It is said that the largest-scale pollution caused in Japan is due to herbicides sprayed on water rice-fields.
Moreover, it is reported that many foods contain dioxins. It is also reported that dioxins are contained in: fishery products caught in South Vietnam; garden vegetables, fruits, milk and etc. which were polluted in the accident caused in Italy in 1976; and mother""s milk tested recently not only in Japan but also in European countries.
The toxicity of dioxins is the strongest of all synthesized chemical substances (stronger than sodium cyanide). It may be no toxic material having stronger toxicity per molecule than that of dioxins except botulinus toxin.
It is reported that the exposure of dioxins causes diseases including melanoderma, myalgia, polyneuritis, cold tolerance lowering disease, liver malfunction accompanied by hepatomegaly in addition to the aforementioned chloracne. There is also a report referring to another diseases caused by the application of dioxins such as atrophy of the thymus, atrophy and necrosis of the testis, generation of abnormal spermatocyte, hypertrophic gastritis and etc. It was found that these diseases result from occupational exposure of highly densed dioxins and dioxins exposing test to Primates. Further, it was found by the animal test that dioxins exhibit teratogenicity, embryotoxicity, carcinogenicity, cocarcinogenicity, genotoxicity and other symptoms.
Recent research report tells that dioxins taken into the body are metabolized slowly. The rat test shows that the half-life of the excretion is about 17 days and that dioxins are discharged out through feces, urine and breath. This measurement has little error in spite that microanalysis is employed because of using a radioactive isotope. Further, the toxicity of dioxins has been studied biochemically, and mainly, the toxicity due to enzyme inhibition has been made clear thereby.
4.  less than Decomposition and Migration of Dioxins in a Dioxins-Containing Environment greater than 
It is reported that biodegradation (organic decomposition by the complicated works of organisms) of dioxins is considerably little, but this doesn""t mean that dioxins are never biodegraded. The result on the above study is different depending on the reporters and does give no clear solution now.
It is known that light of UV region is the most effective to light-decomposing (cutting a chemical bond by light) dioxins. The sunlight decomposition is the most effective of all the natural decompositions. On the other hand, there are many research reports telling experimental results of light-decomposing dioxins under various physical conditions.
Further, the condensation of dioxins also has been observed in the body of animals.
It is reported that plants also condense dioxins contained in soil, but the concentration of dioxins contained in fruits and leaves is lower than expected, which may probably be due to the sunlight decomposition of dioxins.
5.  less than Dioxins Treatment and Purge/Purification greater than 
The treatment of Dioxins has been put into practice conventionally by dumping or filling into a disused pit or tunnel before covering the surface of the port with concrete, or by dumping into sea after solidification with concrete.
It is said that the cost accompanied by the above treatment is about half a million dollars in U.S. for treating the quantity of 3,000 barrel (1 barrel: 120 to 160 litters) held in drum cans so as not to leak out.
There are 3 methods mentioned below which have been conventionally applied on a large scale for removing dioxins.
The first method is removal by incineration that has been developed for the purpose of treating harmful substances having strong toxicity such as agricultural chemicals. The decomposition ratio is different depending on operational conditions of an incinerator. It is said that it takes 21 seconds at 700xc2x0 C. and that a decomposition ratio of 99.5% can be achieved at 800xc2x0 C. The United States Air Force put the largest-scale treatment into practice on the center of the Pacific Ocean using a large-sized incinerator mounted on a chemical tank vessel storing 10,400 tons (not less than 2 million gallon) of herbicide oranges. Its operational conditions are reported as follows. Mean burning temperature: 1,500xc2x0 C., furnace residence time: 1 second, and the concentration of oxygen contained in flue gas: not less than 3%. The combustion efficiency under these conditions was estimated at 99.9%.
As an extension of the removal by incineration, a burning test using molten salt was put into practice in 1975 in U.S. This method has the merit of letting a sample keep at high temperatures for a long time, and as a result of the test, a high decomposition ratio was reported.
Further, decomposition by applying high frequency plasma was reported in 1978 at first. This method is for decomposing dioxins in a short time due to the high reactivity of high temperature plasma resulting from oxygen atoms, and its laboratory-level research was put into practice. It is reported that this method is effective to decomposing not only dioxins but also other stable chemical substances such as PCB etc.
As a decomposition method, photodecomposition is proposed in addition to the combustion. This is a method of applying UV light to a sample kept in an easily photodegradable state. Recently, proposal and experiment have been made to promote the decomposition of dioxins by emitting light of a frequency resonant with the dioxins to cause the isolation of the atoms of the dioxins (corresponding to IR wavelengths) into combustion gas.
The treatment with radial rays also has been studied. This can be regarded as one of the extended photodecomposition technologies. By applying 106 rad of radial rays to dioxins mixed in a solvent of ethanol, acetone, dioxisane or the like, a decomposition ratio of 97% was achieved. However, it was pointed out from the results yielded by a series of experiments that this method is extremely ineffective for decomposing the dioxins mixture and causes the increase of costs. All the aforementioned methods belong to a physical method.
In addition to the above methods, a method of treating dioxins by combustion after absorption by activated carbon also has been studied for treating low enriched dioxins, but this method isn""t applied on a large scale now.
The second method is a chemical one, and plural methods belonging thereto have been proposed.
These methods include, for example,
a) ozone treatment (blowing ozone into a solution containing dioxins),
b) decomposition with iodine chloride (decomposing dioxins by adding iodine chloride thereto after condensing dioxins and changing the condensed dioxins into colloid with a surfactant),
c) wet air oxidation (putting a sample into water before treating under pressures ranging from 40 to 140 atmospheres at temperatures ranging from 150 to 350xc2x0 C. Recently, this method is called as xe2x80x9ccritical water treatmentxe2x80x9d),
d) catalytic dechlorination (reductively depriving chlorine atoms from dioxins using a catalyst), and the like.
However, all of these chemical treatments are in an experimental stage at pilot plant now, and not put into practice on a massive scale. Their characteristic point is to treat the whole contents simultaneously, and they become effective in case of containing dioxins at high concentration.
The third method is biological treatment. For example, dioxins treatment with bacteria is still in the basic research level now, and researches applying this treatment to soil, drainage system and the like are going on. Then, a water treatment apparatus is proposed that has been devised in many ways for increasing the activity of bacteria in soil. These researches are under way under the prerequisite of treating at low concentration.
Currently, dioxins contained in agricultural chemicals and the like have been checked very strictly to decrease their amount. However, the generation of dioxins in a refuse incinerator becomes a big subject of discussion now. This depends on a reason that many chemical substances become wasted out of home as a standard of living is improved to generate dioxins proportionally thereto in the incineration facilities through the refuse incineration process.
The following is explanation of the problems occurring mainly in case of putting the aforementioned conventional methods of removing/treating dioxins into practice in a refuse-incinerating facility or the like.
In a refuse-incinerating facility, a great number of chemical substances are contained because of treating by combustion of various refuse wasted out of home and etc. Accordingly, there is a possibility that the chemical substances of the 1st and 3rd groups explained in the aforementioned paragraph 1 are mixed.
Further, in a refuse-incinerating facility, combustion temperature cannot be elevated so much. This depends on a reason that refuse is not always fit to be burnt. Accordingly, the combustion temperature may be around 800xc2x0 C. at most. Further, the residence time of the combustion gas cannot be prolonged so much. Accordingly, it is expected also by the past experiments that the possibility of generating dioxins is high. It is recognized now that the surest treating method is to attach an afterburner to the chimney of an incinerator, to inject fuel such as petroleum and the like through the afterburner, and then to burn again at high temperatures.
Taking the above matters into consideration, the method stated in the above paragraph 5 is checked again as follows.
At first, the high temperature burning method is in a sense the same with that put into practice by the United States Air Force in the Pacific Ocean subject to being directed in all refuse-incinerating facilities. However, it takes too much cost for burning refuse by applying this method. This is caused by fuel cost required for heating up to high temperatures and the short life of an incinerator shortened by the high temperatures. Accordingly, it is difficult to put this method into practice.
On the other hand, the method using a molten salt or plasma is certainly effective in case of containing dioxins at high concentration, but this method also requires too much operational cost. Particularly, in case of applying plasma, temperature of the plasma-emitted spot exceeds ten thousand degree. This method is not practicable because high cost is required for raising temperatures. Accordingly, it is actually difficult to apply this method to refuse incineration. In case of raising up the temperature of electrons constituting plasma partially, it can be easily imagined that the decomposition ratio of dioxins becomes lowered.
Conventionally proposed photodecompositions, i.e., methods of applying UV rays, radioactive rays and IR rays are studied now. Among them, so far as the radioactive rays are concerned, introducing a radioactive generator, which emits very strong radioactive rays, into usual civil facilities like a refuse incineration facilities in itself causes problems in control and safety and substantial rise in treating cost thereby.
Though UV and IR rays are much absorbed by other molecules than dioxins in an incinerator (the absorbance of IR and UV rays is basically large in the air), improvement in efficiency of decomposing dioxins is expected if dioxins are contained at high concentration in the air. However, in this method, it is necessary to set up special lamps and laser oscillators for the emission of UV or IR rays, and the fact that the oscillating tube by itself is high in cost causes a big problem.
On the other hand, considering the cost of activated carbon and the property that activated carbon absorbs chemical substances in addition to dioxins, it will be necessary to review the aspect of costs arising in the separation by absorption with activated carbon in the future.
Next, the chemical and biological treatments referred to in the above paragraph 5 will be considered as follows. In case of the chemical treatment, all the contents are principally treated at the same time. Accordingly, refuse, which does not require such treatment in itself, are also treated inevitably. Thereby, it is expected that costs become very high.
On the other hand, the biological treatment cannot be applied in a refuse-incinerating facility because of using bacteria.
Accordingly, the present invention has been made in consideration of the aforementioned problems involved in the prior art. It is an object of the present invention to provide a process and apparatus for treating dioxins that assure low cost and high efficiency and are suitable for application to refuse incineration.
According to a first aspect of the present invention, decomposition of objective chemical substances to be removed such as dioxins is made by applying electromagnetic wave to an objective chemical substance and/or a material containing the objective chemical substance to heat the objective chemical substance to be removed selectively.
According to a second aspect of the present invention, decomposition of dioxins is made by applying electromagnetic wave to combustion gas generated and held in a refuse incinerator to heat selectively dioxins contained in the combustion gas. Further, decomposition of dioxins is made by applying electromagnetic wave to fly ashes in a refuse incinerator to heat selectively dioxins contained in the fly ashes.
According to a third aspect of the present invention, an electromagnetic wave oscillator is provided so as to apply electromagnetic wave emitted to a dioxin-containing combustion gas in an incinerator. Other applicable means and methods in the present invention for solving the aforementioned problems are just as disclosed in each of the appended claims.